of bomb scares across the country that grounded planes and shut down campuses. Abc's pierre thomas is in washington with the latest on the mysterious wave of threats. People want to know what's going on here. Reporter: Good morning, robin. The fbi is racing to find behind those threats, which disrupted the lives of thousands over the last 48 hours. In richmond, virginia, a bomb threat shuts down the city's airport for 3 1/2 hours tuesday. The threat came in by phone. The caller claiming to be with the taliban. A security guard came by and looked at me and said, ma'am, you need to put down the coffee and leave the building. Reporter: Around the same time at princeton university in new jersey. Developing news out of princeton. The campus remains evacuated after a bomb threat. Reporter: Students and teachers were evacuated after separate bomb threats against multiple buildings on campus, splacing thousands. Something's going on. It must be something showing up that they're shutting everything down. Reporter: And in atlanta, two other bomb threats led to massive evacuations. Tuesday's threats came after a plane was forced to make an emergency landing in phoenix overnight monday. F-16 fighter jets escorting the flight from l.A., After someone called in a threat. As in richmond, the caller claimed to be with the taliban. The callers will impersonate the taliban, al qaeda or an extremist group. They believe it gives their call more credibility. And law enforcement will ratchet up their reaction and response to it. Reporter: The fbi is now trying to determine if the threats, which were all made by phone, are linked. No bombs were found and the threats were bogus. But these hoaxes are treated seriously because they burn up so much time in law enforcement resources. Such threats are federal crimes. Maximum penalty, five years in jail, george.

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